1. Field of the Invention
This invention relates to a control method for controlling the output (e.g., the speed of revolution of a servo motor or the opening of a flow rate control valve) of a controlled system (e.g. a servo motor or a flow rate control valve) in response to a control value, and a controller used in the embodiment of this control method.
2. Description of the Prior Art
Control of various physical quantities is carried out in a wide range of fields including temperature and humidity control using air conditioners, tape speed control for video and audio cassette tape recorders using servo motors, tank level control done by controlling flow rates of fluids using fluid-control valves, along with hydraulic, pneumatic and other types of pressure control, torque control, positioning control, and voltage, current and power control.
There are two methods of controlling these physical quantities, namely open-loop control and feedback control. Open-loop control has good response to the controlled variable (e.g. tape speed or another physical quantity to be controlled) but has a disadvantage in that it cannot eliminate all error between the set point for the controlled variable and the actual value of the controlled variable. On the other hand, feedback control is able to bring the actual value of the controlled variable into agreement with its set point, but has the disadvantages of slow response and a large amount of ringing which occurs if attempts are made to improve response.
Before describing the details of open-loop control and feedback control, the attached drawings will be briefly described.